The present invention pertains to multi-port conference circuit arrangements and more particularly to echo suppression techniques for use with interconnecting a large number of conferees.
In modern telecommunications, large numbers of conferees may be lashed up (interconnected) to all participants (conferees) in one common telephone call. The number of conferees in one conference call may be large, approximately 20 to 25 conferees. Each of the conferees is connected to the switching network via either a line circuit or a trunk circuit. These line or trunk circuits are connected to the switching network. In a digital switching network a codec/filter converts incoming analog signals to digital signals and outgoing digital signals to analog signals.
The line and trunk circuits include hybrids. These hybrids make two wire to two wire connections in the case of line circuits and two wire to either two wire or to four wire connections in the case of trunk circuits. One of the functions of the hybrid is to balance the line impedance to the subscriber. However, since perfectly balanced hybrids are very difficult or impossible to construct, feedback occurs through a summing junction of the conference circuit.
When large numbers of conferees are interconnected, such as 10 or more, the feedback through the summing junction is added and the gain through operational amplifiers approaches unity. When this occurs, the circuit begins to sing and the conferees are not able to hear the speaker.
Accordingly, it is an object of the present invention to provide a digital voice activated switch for preventing excessive feedback through summing junctions of a conference circuit arrangement.